Hitherto, various gases and oils such as industrial gas, natural gas and petroleum fractions are presented for desulfurization process in order to eliminate adverse effects of sulfur contents contained therein, and are put in use after removal of sulfur contents. In certain processes using these hydrocarbons as materials, metal or noble metal catalysts are used as a catalyst of downstream, and these catalysts are generally susceptible to sulfur poisoning. Many metals are known to form surface sulfides on their surface even if sulfur of low concentration below the ppm order. For example, as unveiled by the studies of McCarty et al. (J. Chem. Phys. Vol. 72, No. 12, 6332, 1980, J. Chem. Phys. Vol. 74, No. 10, 5877, 1981), the sulfur adsorptivity of Ni and Ru is very strong, and therefore if the sulfur content in the material is about 0.1 ppm, the surface of Ni or Ru catalyst is covered almost entirely with sulfur in the equilibrium state (sulfur coverage 0.8 or more). As for other metals, it is reported that surface sulfides are likely to be formed and that sulfur poisoning occurs very easily. Therefore, to prevent sulfur poisoning of downstream catalysts and enhance the process economy, it is desired to lower the sulfur contents in materials as much as possible.
As the method for removing sulfur compounds contained in hydrocarbon materials, various methods have been known, and a general method is the hydrodesulfurization method of hydrogenating sulfur compounds to form hydrogen sulfide, and removing this hydrogen sulfide by using adsorbent such as zinc oxide. In this hydrodesulfurization method, however, when hydrogenating sulfur compounds into hydrogen sulfide, much hydrogen (for example, addition of hydrogen by about 0.05 to 0.1 to the material by molar ratio) is required, the unsaturated hydrocarbon itself, or the unsaturated hydrocarbon such as olefin contained in material hydrocarbon is also hydrogenated. Therefore it is not proper in the case of hydrocarbon which may be hydrogenated. For example, when refining ethylene, propylene, or other olefin compounds, or if not desired to decrease the olefin content in order to maintain the octane value in hydrocarbon material such as gasoline with high contents of unsaturated hydrocarbons such as olefin, it is not proper to employ the hydrodesulfurization method.
The Japanese Patent Unexamined Publication No. 196829/1984 and No. 52041/1990 disclose methods of desulfurization of olefinic hydrocarbons by using adsorbing desulfurizing agent of zinc oxide compound, but in these methods of desulfurization, although it is effective for sulfur compounds such as hydrogen sulfide, mercaptan and COS, the desulfurization effect is small in other sulfur compounds such as thiophene and sulfides.
Other method of desulfurization without hydrogenating olefin by hydrolytic desulfurization method is known, but the sulfur compounds that can be desulfurized are limited to carbon disulfide and carbonyl sulfide.
Besides, adsorption desulfurization by activated carbon or the like may be considered, but hydrocarbon contained in the hydrocarbon material is absorbed at the same time, almost all of the sites that should be adsorbed by the sulfur compound, in principle, cannot be utilized, and if attempted to keep a sufficient sulfur adsorption amount, a huge volume of activated carbon is required.
It is hence a primary object of the invention to present a method of desulfurization capable of desulfurizing at high degree, while suppressing hydrogenation of unsaturated hydrocarbon by solving the problems of the conventional methods of desulfurization.